Immersive View Went Beyond 3-D On SPR Project

If you think computer-driven, immersive visualization with its splashy colorful displays belongs in the just-another-pretty-face category, think again.

This high-end technology is evolving as a powerful tool to educate and inform not only in-the-know professional types but the ordinary citizen as well.

Consider, for instance, its potential to allay the pervasive anxiety and fear often harbored by those who have an underground storage facility for a neighbor. A model of the facility created using immersive visualization software can be used to demonstrate to the public the high level of understanding on the part of facility operators regarding the site's subsurface.

"To the layperson who is unaccustomed to evaluating the scientific information that created the model, immersive visualization is the ideal way to display these underground areas to reassure people about the integrity of a particular site," said Ken Weisenburger, exploration advisor at Continuum Resources.

And it offers a new, sophisticated approach to operate such areas.

The most common underground storage sites are depleted reservoirs in oil and gas fields, aquifers and salt formations -- both bedded salt and salt domes.

The entity that perhaps is most synonymous with salt cavern hydrocarbon storage is the federal government's Department of Energy (DOE), which operates the Strategic Petroleum Reserve (SPR) sites where liquid and gaseous hydrocarbons are stored in underground caverns in salt domes. The newest SPR storage site is at the Big Hill salt dome in Jefferson County, Texas, about 20 miles southwest of Beaumont.

The facility, which is one of the four major SPR sites, consists of 14 underground solution-mined storage caverns that have a combined storage capacity of 160 million barrels of crude oil.

If you think computer-driven, immersive visualization with its splashy colorful displays belongs in the just-another-pretty-face category, think again.

This high-end technology is evolving as a powerful tool to educate and inform not only in-the-know professional types but the ordinary citizen as well.

Consider, for instance, its potential to allay the pervasive anxiety and fear often harbored by those who have an underground storage facility for a neighbor. A model of the facility created using immersive visualization software can be used to demonstrate to the public the high level of understanding on the part of facility operators regarding the site's subsurface.

"To the layperson who is unaccustomed to evaluating the scientific information that created the model, immersive visualization is the ideal way to display these underground areas to reassure people about the integrity of a particular site," said Ken Weisenburger, exploration advisor at Continuum Resources.

And it offers a new, sophisticated approach to operate such areas.

The most common underground storage sites are depleted reservoirs in oil and gas fields, aquifers and salt formations -- both bedded salt and salt domes.

The entity that perhaps is most synonymous with salt cavern hydrocarbon storage is the federal government's Department of Energy (DOE), which operates the Strategic Petroleum Reserve (SPR) sites where liquid and gaseous hydrocarbons are stored in underground caverns in salt domes. The newest SPR storage site is at the Big Hill salt dome in Jefferson County, Texas, about 20 miles southwest of Beaumont.

The facility, which is one of the four major SPR sites, consists of 14 underground solution-mined storage caverns that have a combined storage capacity of 160 million barrels of crude oil.

When the decision was made recently to drill an additional five caverns there, the underground storage technology support group for the SPR -- Sandia National Laboratories -- approached Continuum to construct a model of the site incorporating all available geological and geophysical data.

"Sandia wanted to confirm that the new caverns were placed far from the edge of the salt," said Continuum vice-president for technical services, Peter Duncan. "There was some idea there was a salt overhang on the northwest part of the dome, and they needed to know.

"They had a lot of well logs around the salt dome with tops picked, and a geologist had done some work on where the salt was, and a geophysicist had worked on defining the caprock," he said. "But no one had integrated anything into a single study to know exactly where the salt was."

The 'Invaluable Component'

To build a model of the salt body, the company used high resolution 2-D data to image the caprock, and subsurface data from 90-plus wells were used to determine the location of the salt and the caprock.

To image the salt's deep flanks, the project team members used nine square miles of non-exclusive 3-D data, which Sandia licensed from Veritas.

Gravity data acquired from the public domain were a key ingredient in the project.

"We had the near-surface issue of the caprock, and we knew the salt was at least 14,000 to 15,000 feet thick," Weisenburger said, "so we felt from the start that gravity would be an invaluable component to help integrate all the different data sets together.

"After the initial interpretation that was done strictly from subsurface data and available seismic data, we created the first model using gravity data."

On this first pass, the calculated residual gravity -- the difference between the modeled gravity response and the true earth response -- was too high, indicating there was too much salt in the model.

Three iterations were performed to improve the gravity residual, making it smaller. In the iterative exercises, the salt model was changed principally down along the sides of the salt wall and by bringing the base of the salt upward.

The final model revealed a smaller body of salt than originally thought.

"This was important to Sandia," Duncan said, "because there's less salt body for caverns."

Modeling of the high-density caprock showed a major solution graben in the caprock and numerous faults that correlate to regional faults interpreted with the 3-D data. The top of the salt, however, displays none of these complexities. This suggests the fault displacements have healed within the ductile salt, so new caverns can be located without risk of active faulting.

Duncan emphasized the model is a minimum salt model because they wanted to err on the conservative side.

Even so, all of the existing and proposed cavern locations were shown to be within the safety zone of 500 feet from the salt walls.

Incorporating the Data

To incorporate the gravity data into the project, Continuum capitalized on GETECH's expertise in 3-D gravity modeling.

The company has used gravity data to model all of the salt domes from Matagorda County in Texas to the mouth of the Mississippi River in Louisiana, according to geophysicist Bob Weber.

"GETECH's gravity modeling added important constraints on the size of the Big Hill salt body," Weber said, "and I think it's significant that Continuum looked at hard science to come up with a solution. Maybe it's part of what's happening now in the industry, that people are more willing to look at all of the information."

Utilizing an immersive visualization environment to view the end result of using multi-source information provides a one-stop viewing shop, where representatives of the various disciplines can assemble to evaluate and understand the individual contributions

"There are a variety of professionals using the modeled data, including mining engineers and hydrocarbon storage specialists, who may not have seen seismic data before," Weisenburger said, "and those little wiggles have little meaning to those who haven't seen seismic.

"Here, they are looking at the physical model of the salt itself and can see how everything relates."

The combo of the model and the proprietary immersive visualization software used for the project provides a powerful site maintenance tool as well. For instance, the software is time dependent, so it's possible to make projections into the future, according to Weisenburger.

Say, for example, a site has a cavern that is sloughing, or an area that might endanger other sites. This can be extended into the future, showing where it would start to create a risk -- and thus enable the operator to deal with the potential problem in a proactive rather than a reactive manner.

The actual caverns that are in the Big Hill salt model as it exists now are idealized cylinders. Via a recently-inked agreement with Sandia, Continuum will integrate Sandia's sonar data from the existing caverns into the model to provide the true configuration of each cavern.

"Hopefully, once we get the sonar into the model and DOE sees it, it will lead to future work of doing this for all of the domes, especially if we have seismic and gravity data," said Cecelia Williams, principle member of the technical staff at Sandia. "The 3-D model of the dome was something DOE had wanted for years, and they had never got quite what they wanted."